Recently, in semiconductor manufacturing processes, isopropanol (IPA) has become used for drying semiconductor substrates after washing with water. When metal ions have mixed into IPA used for drying semiconductor substrates after washing with water, metal remains on semiconductor substrates, leading to a decrease in the yield. Thus, as IPA used for drying semiconductor substrates after washing with water, high-purity IPA having an extremely low content of metal ions is required.
In the case of carrying out solution polymerization by dissolving monomers in an organic solvent, if metal ions are present in the organic solvent, metal mixes into a polymer as a product and may be responsible for a decrease in the performance. Accordingly, also as organic solvents used as a solvent for monomer polymerization, high-purity solvents having an extremely low content of metal ions are required.
In production facilities in which a large amount of organic solvents is used for washing various materials to be cleaned, dissolution and dispersion of functional compounds, and the like, recovery and recycling of organic solvents used for washing and the like are required without discharging them outside, from the viewpoint of considering the environment. For this reason, in order to recycle recovered organic solvents, it is required to remove metal ions mixed in the solvents due to washing or the like from the recovered organic solvents.
An exemplary method for purifying an organic solvent is purification by distillation. However, distillation requires a large facility and enormous energy, leading to an increase in the purification cost.
In contrast, a method including use of a particulate ion exchange resin, specifically, purification by contacting an organic solvent with a particulate ion exchange resin as described in Patent Literature 1 or 2 below, which only requires allowing an organic solvent to pass through an ion exchange resin tower, can achieve convenient purification and keep the purification cost low, as compared with distillation.